Ternary refrigerant compositions containing fluorinated ethers as replacements for R-22

ABSTRACT

Refrigerant compositions include mixtures of at least three different components, including a fluorinated ether with at least one of a second fluorinated ether, an ether and a fluorinated hydrocarbon. Also, methods for cooling a body include compressing such a refrigerant composition and bringing the body into heat transfer relation to it. The disclosed refrigerant compounds have refrigerant-significant properties similar to those of R-22, and they can be employed in place of or as drop-in substitutes in refrigeration apparatus designed for R-22 application.

BACKGROUND

1. Field of the Invention

This invention relates to refrigerants and, particularly, to mixturessuitable for use as substitutes for hydrochlorofluorocarbons (HCFCs) andchlorofluorocarbons (CFCs) in refrigeration. In particular the ternarycompositions include components selected from fluorinated ethers, ethersand fluorinated hydrocarbons.

2. Description of Related Art

In recent years it has been suggested that release of certainhydrochlorofluorocarbons and chlorofluorocarbons may have adverselong-term effects on the earth's atmosphere. Particularly, thesecompounds are thought to undergo a ultraviolet radiation induceddecomposition in the upper atmosphere, releasing chlorine atoms whichare thought to react with ozone. The reaction of chlorine with ozonecould reduce the extent of the protective stratospheric ozone layer.Depletion of the ozone layer could permit increased penetration ofharmful ultraviolet radiation through the upper reaches of theatmosphere, with deleterious effects on the biosphere. Although thistheory is not universally accepted, there has been a growing movement ofinternational scope toward control of the production and use of certainCFCs and HCFCs.

Particularly, government regulation is forcing a phasing out of certainchlorine-containing refrigerants, and replacement of them withenvironmentally safer compounds. Accordingly, considerable effort hasbeen directed toward finding alternatives for CFCs and HCFCs. Suitablerefrigerant substitutes would be expected to have both a lower potentialto damage the atmosphere and an acceptably high performance in theparticular refrigeration systems in which they are intended asreplacements for the conventional or “first-generation” CFC or HCFCrefrigerants. For example, Sherwood U.S. Pat. No. 5,713,211 describescertain fluoroethers said to be useful in secondary loop refrigeration.

Thus far, no single compound has yet proven completely satisfactory as areplacement for any of the conventional CFC and HCFC refrigerants. Forexample, HCFC 134a (see below) has proven to be a satisfactorysubstitute refrigerant for CFC-12 in most but not all applications. Muchof the developmental effort in this field has been directed towardfinding suitable mixtures, and particularly azeotropic or azeotrope-likemixtures. For example, Lunger et al. U.S. Pat. No. 5,670,079 describesnon-flammable azeotropic and azeotrope-like mixtures of a hydrocarbonand a fluorine-containing molecule, in which the atmospheric boilingpoints of the components differ by at least 20° C. Bivens et al. U.S.Pat. No. 4,810,403 describes refrigerant mixtures of three or moreselected halocarbons, each one after the first having a successivelyhigher boiling point, and having a temperature/pressure relation likethat of dichlorodifluoro methane (CCl₂F₂, FC-12). Gage et al. U.S. Pat.No. 5,650,089 describes binary refrigerant mixtures, which may beazeotropic (or azeotrope-like) or zeotropic, in which the components areselected from certain hydrofluoroethers, hydrofluorocarbons, andhydrocarbons. Klug et al. U.S. Pat. No. 5,605,882 and U.S. Pat. No.5,648,016 describe azeotropic and azeotrope-like mixtures of afluoroether and a hydrofluorocarbon, said to be useful among otherapplications as refrigerants. Minor et al. U.S. Pat. No. 5,443,880described binary refrigerant mixtures in which one of the components isa sulfur-containing compound. Pearson U.S. Pat. No. 5,108,637 describesrefrigerants including ternary mixtures in “nonflammable proportions”,which may or may not be azeotropic. Shiflett U.S. Pat. No. 5,709,092describes nonflammable near-azeotropic or essentially constant boilingmixtures of at least two components, and particularly ternary mixturesof certain fluorocarbons, said to be especially useful as supermarketcase refrigerants. All the patents and other publications cited in thisapplication are hereby incorporated herein in their entirety.

Chlorodifluoromethane (CHClF₂, R-22) is one refrigerant for which asuitable substitute has been especially difficult to find.Refrigerant-significant parameters of a refrigerant mixture suitable foruse as a R-22 substitute include: low boiling point (T_(b) for R-22 isabout −41° C.); high critical temperature (T_(c) for R-22 is about 96°C.); critical mixing temperature well below the boiling point; and anacceptable flammability limit. Preferably the refrigerant issubstantially non-corrosive to parts and fittings of the refrigerationapparatus which it contacts in use.

The situation remains that improved replacement refrigerants havingoptimum properties have not been reported. The present inventionprovides improved replacement mixtures.

SUMMARY OF THE INVENTION

We have discovered that certain combinations of three or more differentcompounds can provide refrigerant mixtures havingrefrigerant-significant properties that approximate those of R-22 and,accordingly, these mixtures are highly suitable as a drop-in substitutein R-22 refrigeration applications. The mixtures include at least onefluoroether, which may be a perfluoroether, and one or more of a secondfluoroether, an ether and a fluorinated hydrocarbon. Preferred R-22substitutes according to the invention are near-azeotropic, as these donot fractionate significantly over the range of temperature in use.Accordingly, in one general aspect the invention features a refrigerantcomposition that is a mixture of at least three different components, inwhich at least a first one of the components is a fluorinated ether andeach of the second and the third components is a fluorinated ether, anether and a fluorinated hydrocarbon. In some embodiments, each of atleast three components is present in a proportion of at least 10 molepercent, and more usually one or more (most usually all) of at leastthree components is present in a proportion of at least 20 mole percent.It is understood that the total mol % of the ternary mixtures describedherein must equal 100%.

In some embodiments the fluorinated sulfur-containing compound, ifoptionally present, is a fluorinated methyl sulfide. Particularfluorinated methyl sulfides include bis(trifluoromethyl) sulfide,CF₃SCF₃ (116S); and trifluoromethylsulfur pentafluoride, CF₃SF₅ (18S).

In some embodiments the fluorinated hydrocarbon, where present, has theformula C_((x))F_((y))H_((2x+2−y)), where x=1 or 2, and 1≦y≦2x.Particular fluorinated hydrocarbons include 1,1,1,2-tetrafluoroethane,CF₃CH₂F (HFC-134a); 1,1,1-trifluoroethane, CF₃CH₃ (HFC-143a);1,1-difluoroethane, CH₃CF₂H (HFC-152a); fluoroethane, CH₃CH₂F (HFC-161);and difluoromethane, CH₂F₂ (HFC-32).

Embodiments of the invention that may provide particularly usefulperformance in R-22 refrigerant applications include mixtures of, forexample: (218E/trifluoromethyl sulfur pentafluoride/152a) in molarproportions, e.g, (0.45/0.10/0.45); (218E/143aE/134a) in molarproportions, e.g., (0.35/0.35/0.3); (218E/143aE/161) in molarproportions, e.g., (0.333/0.333/0.333) or (0.40/0.40/0.20);(218E/134a/161) in molar proportions, e.g., (0.333/0.333/0.333);(125E/32/134a) in molar proportions (0.33/0.33/0.34); (125E/32/152a) inmolar proportions, e.g., (0.33/0.33/0.34); (125E/143a/134a) in molarproportions (0.33/0.33/0.34).

In preferred embodiments the refrigerant composition is azeotropic orazeotrope-like. That is, it is a constant-boiling or substantiallyconstant-boiling mixture of two or more substances that tends not tofractionate upon evaporation. Accordingly, the vapor produced by boilingor evaporation of the azeotropic or azeotrope-like mixture has the sameor substantially the same composition as the liquid.

In another general aspect the invention features a method for cooling abody, by compressing a refrigeration composition according to theinvention and bringing the body into heat transfer relation to it. Therefrigeration compositions of the invention are effective drop-insubstitutes for conventional CFC or HCFC refrigerants such as R-22, andcan be employed in refrigeration apparatus designed for use with suchconventional refrigerants, without significant retrofit or significantmodifications. Some retrofit or modifications include, but are notlimited to, compressor lubricant oils may need to be changed.Accordingly, in another general aspect the invention features arefrigeration system, including refrigeration apparatus configured anddimensioned for use with refrigerant R-22, charged with a refrigerantcomposition of the invention.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENT

Definitions

As used herein:

“Fluorinated ether” refers to the fluorinated ethers used in this art.Some are identified by a convention:

Term Fluorine - Containing 18S Trifluoromethyl pentafluoride R22Chlorodifluoromethane 32 Difluormethine 116S Bis(trifluoromethlysulfide)125 Pentafluoroethane 125E Pentafluorodimethyl ether 134a1,1,1,2-Tetrafluoroethane 143a 1,1,1,-Trifluoroethane 152a1,1-Difluoroethane 161 Fluoroethane 218E Perfluoromethyl ethyl ether

Two-component mixtures having as one component a very highly fluorinatedether and as another component an HFC or ether with a low fluorinecontent may have boiling points and critical temperatures approachingthose of R-22, but these are usually not miscible over the range oftemperatures and pressures they encounter in use. We have discoveredthat admixture of a third component, particularly an ether, having afluorine content between that of the first two components, can providefor improved miscibility and better refrigerant-significantcharacteristics. Usually, the highly fluorinated ether component hasmore fluorine atoms than hydrogen atoms per molecule, and may in someembodiments be perfluorinated; and a molecule of the component havingthe lowest fluorine content has fewer fluorine atoms than hydrogenatoms.

Particularly, for use as R-22 substitutes, preferred mixtures have aboiling point lower than −30° C., usually below about −32° C., stillmore usually below about −33° C. The boiling points are calculated frommeasured vapor pressure data using the following relation between Kelvintemperature (T) and the vapor pressure (P):

1n P=A+B 1n T+C/T,

in which A, B, and C are empirically derived constants.

Particularly for use as R-22 substitutes, preferred mixtures have acritical temperature higher than about 70° C., still more usually higherthan about 80° C., and most usually in the range about 85-100° C. Thecritical temperatures (T_(c)) of the mixtures are measured by slowlyraising the temperature of the sample in a sealed tube untildisappearance of the meniscus is observed. Alternatively oradditionally, the critical temperature (T_(c)) can be estimated from themeasured critical temperatures T_(ic), of the pure components and thecomponent mole fractions X_(ic) using the relation (for threecomponents, i=1,2,3):

T _(c) =X ₁ T _(1c) +X ₂ T _(2c) +X ₃ T _(3c).

Preferred mixtures have a critical mixing temperature below the boilingpoint, usually at least about 5° C. below the boiling point.

The mixtures preferably are substantially non-flammable. Exceptions mayinclude mixtures that contain both E-125 and R-161, and mixtures thatcontain both E-125 and R-152a. Generally, mixtures in which the fractionof C—F and S-F bonds exceeds the fraction of C—C and C—H bonds aresubstantially non-flammable or have flammability limits that areacceptable for commercial units in the refrigeration industry.

The mixtures preferably are also substantially non-corrosive to fittingsof standard R-22 refrigeration apparatus with which the refrigerantcomes into contact in use.

Preferred mixtures are near-azeotropes; that is, they are characterizedby showing less than about 2% separation at temperatures within theoperational range.

The invention is now described in further detail.

Each of the components employed in the mixtures according to theinvention is known, and either is commercially available in the desiredpurity or can be synthesized to the desired purity using publishedmethods of synthesis. The patent literature in the refrigerant artsdescribes methods for synthesizing the various components, or refers tomethods published elsewhere.

Particularly, where certain of the components may not be readilyavailable commercially, the following methods are suggested.

218E (CAS Reg. No. 665-16-7) by direct fluorination of CF₃OCH₂F₃(prepared by reaction of CF₃OF with vinyledine fluoride), see Sekiya etal., 1990, Chemistry Letters, pp. 767-70.

143aE (CAS Reg. No. 421-14-7) by reaction of methyl fluoroformate withsulfur tetrafluoride, see Aldrich et al., 1964, Jour. Am. Chem. Soc.,Vol. 29, pp 11-15.

125E (CAS Reg. No. 3822-68-2) by electrochemical fluorination ofdimethyl ether (CH₃OCH₃), see Fox et al. U.S. Pat. No. 511,760;Hutchinson U.S. Pat. No. 3,887,439.

116S (CAS Reg. No. 371-78-8) by thermal decomposition of CF₃C(O)OSCF₃,see Haas et al., 1969, Chem. Ber., Vol. 102, pp. 77-82.

SF₅CF₃, trifluoromethylsulfur pentafluoride (CAS Reg. No. 373-80-8) byreaction of methyl mercaptan with either cobalt trifluoride or fluorinegas, see Silvey et al. U.S. Pat. No. 2,697,726; Silvey et al., 1950,Jour. Am. Chem. Soc., Vol. 79, pp. 3624-26.

Compounds 32 [difluoromethane], 161 [fluoroethane], 152a[1,1-difluoroethane], 143a [1,1,1-trifluoroethane], 134a[1,1,1,2-tetrafluoroethane], 125 [pentafluoroethane] are commerciallyavailable and may where necessary be purified by distillation or otherconventional method.

The components may be combined by any of a variety of conventionalmethods to yield a mixture having the desired proportions.

A refrigeration system may be charged with a refrigerant mixtureaccording to the invention by conventional means. Because the mixturesare effective as drop-in substitutes or replacements for R-22, they maybe used to charge any refrigeration apparatus designed for use with R-22refrigerant without retrofitting or mechanical adaptation.

EXAMPLES Example 1 Ternary Mixtures Including at Least Two DifferentFluorinated Ethers

This example, referring to Table 1, shows exemplary ternary mixturescontaining as a first component a fluorinated ether (particularly,perfluoromethyl ethyl ether (218E) or pentafluorodimethyl ether (125E)),and as a second component a different fluorinated ether, lessfluorinated than the first (particularly, trifluoromethyl ethyl ether(143aE). A third component is a fluorinated hydrocarbon or anon-fluorinated ether.

TABLE 1 Mole percentages Components  .35 / .35 / .3 218E / 143aE / 134a .35 / .35 / .3 218E / 143aE / 161  .47 / .265 / .265 218E / 143aE / DME.333 / .333 / .333 218E / 143aE / 152a  .25 / .25 / .5 218E / 143aE /152a  .33 / .33 / .33 218E / 143aE / 161  .40 / .40 / .20 218E / 143aE /161  .35 / .35 / .3 218E / 143aE / 161  .33 / .34. / .33 125E / 143aE /32  .33 / .33 / .33 125E / 143aE / 143a

Example 2 Ternary Mixtures Including a Fluorinated Ether and at LeastOne Fluorinated Hydrocarbon

This example, referring to Table 2, shows exemplary ternary mixturescontaining as a first component a fluorinated ether (particularly,perfluoromethyl ethyl ether (218E) or pentafluorodimethyl ether (125E)),and as a second component a fluorinated hydrocarbon. A third componentcan be a second fluorinated hydrocarbon, different from the first.

TABLE 2 Mole percentages Components .333 / .333 / .333 218E / 134a / 161 .33 / .33 / .34 125E / 32 / 134a  .33 / .33 / .34 125E / 32 / 161  .33/ .33 / .34 125E / 32 / 152a  .33 / .33 / .34 125E / 143a / 134a  .33 /.33 / .34 125E / 143a / 161  .33 / .33 / .34 125E / 143a 152a  .33 / .33/ .34 125E / 134a / 161

Example 3 Ternary Mixtures Including a Fluorinated Ether and aNonfluorinated Ether

This example, referring to Table 3, shows exemplary ternary mixturescontaining as a first component a fluorinated ether (particularly,perfluoromethyl ethyl ether (218E)), and as a second component anonfluorinated ether (particularly, dimethyl ether). A third componentcan be a fluorinated hydrocarbon.

TABLE 3 Mole percentages Components .25 / .25 / .5 218E / DME / 152a

Example 4 Ternary Mixtures Including a Fluorinated Ether and aFluorinated Sulfur-Containing Compound

This example, referring to Table 4, shows exemplary ternary mixturescontaining as a first component a fluorinated ether (particularly,perfluoromethyl ethyl ether (218E)), and as a second component afluorinated sulfur-containing compound (particularly, trifluoromethylsulfur pentafluoride). A third component can be a fluorinatedhydrocarbon.

TABLE 4 Mole percentages Components  .45 / .10 / .45 218E /trifluoromethyl sulfur pentafluoride / 152a .373 / .254 / .373 218E /trifluoromethyl sulfur pentafluoride / 152a  .3 / .3 / .4 218E /trifluoromethyl sulfur pentafluoride / 152a  .25 / .2 / .55 218E /trifluoromethyl sulfur pentafluoride / 152a  .33 / .33 / .34 218E /trifluoromethyl sulfur pentafluoride / 152a

Other embodiments are within the following claims.

While only a few embodiments of the invention have been shown anddescribed herein, it will become apparent to those skilled in the artthat various modifications and changes can be made in the improvedreplacement refrigerant compositions without departing from the spiritand scope of the present invention. All such modifications and changescoming within the scope of the appended claims are intended to becarried out thereby.

What is claimed is:
 1. A refrigerant composition consisting essentiallyof a mixture of three components, each said component being differentfrom the other said components, a first said component being a firstfluorinated ether and each of a second said component and a third saidcomponent being selected from the group consisting of a fluorinatedether, an ether, and a fluorinated hydrocarbon wherein said compositionhas improved miscibility and has less than about 2% separation attemperatures within the operational range.
 2. The refrigerantcomposition of claim 1 wherein said first fluorinated ether has theformula C _((n)) F _((m)) H _((2n+2−m)) O, where n=2 or 3; and 3≦m≦8. 3.The refrigerant composition of claim 1 wherein said first fluorinatedether is selected from the group consisting of perfluoromethyl ethylether, pentafluorodimethyl ether, and trifluoromethyl methyl ether. 4.The refrigerant composition of claim 1 wherein said second component isa fluorinated ether different from said first fluorinated ether.
 5. Arefrigerant composition consisting essentially of a mixture of threecomponents, wherein the first component is selected from the groupconsisting of perfluoromethyl ethyl ether, pentafluorodimethyl ether andtrifluoromethyl methyl ether and said second component is a fluorinatedether selected from the group consisting of perfluoromethyl ethyl ether,pentafluorodimethyl ether and trifluoromethyl methyl ether.
 6. Therefrigerant composition of claim 1 wherein said second component is afluorinated hydrocarbon.
 7. The refrigerant composition of claim 1wherein said second component is an ether.
 8. The refrigerantcomposition of claim 1, wherein said composition is a mixture oftrifluoromethyl pentafluoroethyl ether and trifluoromethyl sulfurpentafluoride and 1,1-difluoroethane.
 9. (The refrigerant composition ofclaim 8, wherein said composition is trifluoromethyl sulfurpentafluoride/1,1-difluoroethane being present in said mixture in molarproportions about 0.45/0.10/45.
 10. The refrigerant composition of claim1, wherein said composition is a mixture of trifluoromethylpentafluoroethyl ether and trifluoromethyl methyl ether and1,1,1,2-tetrafluoroethane.
 11. The refrigerant composition of claim 10,wherein said composition is trifluoromethyl pentafluoroethylether/trifluoromethyl methyl ether/1,1,1,2-tetrafluoroethane beingpresent in said mixture in molar proportions about 0.35/0.35/0.30. 12.The refrigerant composition of claim 1, wherein said composition is amixture of trifluoromethyl pentafluoroethyl ether and trifluoromethylmethyl ether and fluoroethane.
 13. The refrigerant composition of claim12, wherein said composition is trifluoromethyl pentafluoroethylether/trifluoromethyl methyl ether/fluoroethane being present in saidmixture in molar proportions about 0.33/0.33/0.33.
 14. The refrigerantcomposition of claim 12, wherein said composition is trifluoromethylpentafluoroethyl ether/trifluoromethyl methyl ether/fluoroethane beingpresent in said mixture in molar proportions about 0.40/0.40/0.20. 15.The refrigerant composition of claim 1, wherein said composition is amixture of trifluoromethyl pentafluoroethyl ether and1,1,1,2-tetrafluoroethane and fluoroethane.
 16. The refrigerantcomposition of claim 15, wherein said composition is trifluoromethylpentafluoroethyl ether/1,1,1,2-tetrafluoroethane/fluoroethane beingpresent in said mixture in molar proportions about 0.333/0.333/0.333.17. The refrigerant composition of claim 1, wherein said composition isa mixture of pentafluorodimethyl ether and difluoromethane and1,1,1,2-tetrafluoroethane.
 18. The refrigerant composition of claim 17,wherein said composition is pentafluorodimethyl ether/difluoromethane/1,1,1,2-tetrafluoroethane being present in said mixturein molar proportions about 0.33/0.33/0.34.
 19. The refrigerantcomposition of claim 1, wherein said composition is a mixture ofpentafluorodimethyl ether and difluoromethane and 1,1-difluoroethane.20. The refrigerant composition of claim 19, wherein said composition ispentafluorodimethyl ether/difluoromethane/1,1-difluoroethane beingpresent in said mixture in molar proportions about 0.33/0.33/0.34. 21.The refrigerant composition of claim 1, wherein said composition is amixture of pentafluorodimethyl ether and 1,1,1-trifluoroethane and1,1,1,2-tetrafluoroethane.
 22. The refrigerant composition of claim 1,wherein said composition is pentafluorodimethylether/1,1,1-trifluoroethane/1,1,1,2-tetrafluoroethane being present insaid mixture in molar proportions about 0.33/0.33/0.34.
 23. A method forcooling a body, which method comprises the steps of: (a) obtaining thecomposition of claim 1; (b) compressing the composition of step (a); and(c) contacting the body in heat transfer relation to said composition.24. A refrigeration system which comprises: refrigeration apparatuscharged with the refrigerant composition of claim
 1. 25. Therefrigeration system of claim 24, said refrigeration apparatus beingconfigured and dimensioned for use with refrigerantdichlorodifluoromethane R-22.